Process for preventing corrosion during



United States Patent O PROCESS FOR PREVENTING CORROSION DURING DISTILLATION BY ADDING AN ORGANIC PHOSPHITE William L. Fierce, Crystal Lake, and Walter J. Sandner,

Carpentersville, Ill., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application October 29, 1957 Serial No. 692,997

9 Claims. (Cl. 208-348) This invention relates to the processing of a hydrocarv troleum fraction boiling in the naphtha range is further refined at an elevated temperature.

In the manufacture of industrial solvents from crude petroleum oils, selected fractions of the lighter, more volatile constituents of the crude petroleum are chemically refined and separated into various boiling ranges. In preparing the selected fraction there is concomitantly produced during the fractional distillation of the crude petroleum oil a variety of impurities, including undesirable sulfur compounds. A number of these sulfur compounds boiling in the naphtha range have a deleterious effect because they impart to the naphtha distillate certain un desirable odors as well as corrosive properties which cause metal corrosion or the darkening of paints or varnishes. It is, therefore, desirable to pretreat the naphtha distillate prior to the separation of the full boiling range naphtha into the selected fraction. Although a variety of desulfurization processes for the refining of light petroleum products are available, conventional refining techniques involve the treatment of the naphtha distillate in an oxidative-sweetening type of process in which the objectionable sulfur compounds, such as mercaptans, are converted or. transformed into less noisome sulfur compounds which do not affect the usefulness of the naphthas. Examples of suitable processes which are employed in the oxidativesweetening of light petroleum distillates include the doctor treat employing sodium plumbite, the hypochlorite treatment, treating methods using copper-containing reagents, such as copper chloride, or copper oxide, and other processes.

In the distillation of the crude petroleum oil any hydrogen sulfide which may have been contained in the crude oil feed stock is removed in the natural gas or in refinery off-gases. Accordingly, the objectionable sulfur compounds contained in the naphtha distillate from the standpoint of odor and corrosion are generally the mercaptans.

In the oxidative-sweetening process these objectionable sulfur compounds are converted to relatively innocuous organic sulfides or disulfides. In the subsequent distillation step in which the oxidatively-sweetened naphthas are separated into fractions having various boiling ranges, depending upon the end use of the selected distillate, elevated temperatures are employed which result in the reconversion of the unharmful sulfur compounds into noxious sulfur compounds which are corrosive and odorous. This problem is particularly prevalent in the preparation of naphthas which contain components boiling above about 300 F. This condition, however, can also occur in the treatment of lower-boiling naphthas or petroleum fractions, even though special designs are em-.

2,899,387 Patented Aug. '11, 1959 ice ployed in order to avoid excessive skin temperatures on the walls of fractionating columns or other processing vessels in which the high temperatures which produce the conversion of organic sulfide or disulfides into undesirable sulfur compounds are encountered.

To overcome this problem a number of techniques have been developed, wherein an additive composition is introduced into the refining process, in order to prevent the conversion of the relatively innocuous organic sulfides or disulfides to the undesirable mercaptans which produce conditions of corrosion and odor. Suitable agents for this purpose include glycerin, various organic peroxides, such as tertiary butyl hydroperoxide and benzoyl peroxide, as well as compositions consisting of an admixture of an alkylene oxide and an oil-soluble basic salt of a highmolecular-weight organic acid not reactive with the alkylene oxide. According to this invention, an additional expedient has been found which will permit the treatment of oxidatively-sweetened, hydrocarbon compounds containing organic sulfur compounds, including disulfides,

: at temperatures normally effective for the conversion of said compounds to produce noxious sulfur compounds which have a deleterious effect on the odor and corrosiveness properties of the treated hydrocarbon fraction.

It is, therefore, an object of this invention to provide a method for the refining of oxidatively-sweetened, hydrocarbon fractions containing organic sulfur compounds, in cluding disulfides, at elevated temperatures which would normally effect the conversion of these compounds to produce undesirable sulfur-containing products. It is an other object of this invention to effect the distillation of oxidatively-sweetened, hydrocarbon fractions containing organic sulfur compounds, including disulfides, without converting the organic compounds to undesirable sulfurcontaining products. It is another object of this invention to provide a method for preventing the development of odor or corrosiveness in oxidatively-sweetened petroleum liquids during distillation. These and other objects will become more apparent from the following detailed description of this invention.

According to this invention, it has been found that the refining of an oxidatively-sweetened, hydrocarbon fraction containing organic sulfur compounds, including disulfides, can be carried out at elevated temperatures normally effective for the conversion of said sulfur compounds without producing undesirable sulfur-containing products by carrying out the refining process in the presence of an added amount of a non-aromatic, oil-soluble, organic phosphite. In order to effectuate the objectives of this invention it is necessary that not less than about 0.4% by weight of organic phosphite, based on the charge of the hydrocarbon fraction, be employed.

In carrying out the process of this invention, the

7 selected organic phosphite is added to the sulfur-containevent that a batch-wise distillation process is used. This same procedure can be used if the distillation process is carried out continuously. In this instance, however, it is preferred that the necessary amounts of refining agent in the form of organic phosphite be introduced into and admixed with the incoming feed by the continuous in- I jection of the selected phosphite before the feed stock enters the fractionating tower. The organic phosphite which is added to the sulfur-containing hydrocarbon fraction prior to or during the fractionation or refining at an elevated temperature can be any oil-soluble, non aromatic organic phosphite having a boiling point at least as high as the end boiling point of the hydrocarbon fraction being distilled orrefined at an elevatedtemperature. Organic. phosphites having the general tormlllct rfofi-n" Bi -1Q where R, R, and R" are-selected from the group consisting of alkyl or alicycli'c radicals having one to ten carbon atoms or more. t 4

Suitable reagents'include, but are not limitedto, trimethyl phosphite, triethyl phosphite, trien-propyl' phos= phite, tri-Z-propyl phosphite, tributyl phosphite, tI'i'iSD1 butyl'phosphite, triamylphosphite, trihexyl: phosphite, tri-2-ethylhexyl phosphite, triisooctyl phosphite, and tricyelohexyl phosphite Unsymmetrical aliphatic. or ah.- cyelie phpsphites, such as propyl di-n-butyl phosphite, can also be used. 1

F0. faeilitatethe handling 'of the organic phosphite treating agent employed in the process of this inventi n; it is. preferred that the selected phosphite. be a normally liquid product, In the event, however, that solid organic phosphites are available and are. pr ferred. for use, a concentrate obtained by dissolving a. sllfic eut amount of the. organic. phosphite in a por i n f he. hyd ca bon charge. being disti ed or refine can be. sed- The. am unt of'orgenic Phesp e utilized ilL. of depend up n. the ype f hydr carbon fraction being trea ed, as well. as pon the nature and on entrat on of. th sulfur c mp unds Alth ug amoun n ess h n. a ut. 0. by we ght are req ed o efiectuate he ohie ti es f. his inv nt n, the optimumq antity of or anic Phosphite s b st determined experimentall by ng te on small samples obtained from th hy rocarbon fraction which is to be distilled or refined at an elevated temperature. In general, amounts up to about 1.0% by weight are. effective. On the other hand, quantities. as high as. 5.0%. by weight may be. required in exceptional cases.

To. illust ate the in tan in nt on, petroleum naph ha derived from a Mid-Continent crude, having an ASTM boiling range of about 100-400 F. was initially sweetened in an oxidative-sweetcning type process by contacting it with an Attapulgus clay in the presence of cupric chloride, employing a ratio of treating agents of grams 200 mesh Attapulgus' clay, to 0.50 gram of cupric chloride per 700 ml. of naphtha. The treated naphtha was subjected to. the well-known doctor test (ASTM designation D484=4.0) and gave. a negative. test. The naphtha was. divided into a. n mber of samples and he e sa pl s re redis illedat. atmospheric pr sur either in the absence of or the presence of various addi tive materials, including the. organic phosphites employed in the process. of this. invention. The results of hese distillations a e s mmariz d in abular fo m n The unusual or unexpected results which are produced by the. process of this inven i n are. clearly seen fro a review of the data presented in Table I. It will be noted that, in the absence of a selected organic phosphite, the oxidatively-sweetened naphtha became doctor positive in the fractions that were recovered above 60 volume peroent (about. 270 F.) however, when a portion of the doctor negative naphtha was distilled in the presence of 5% by volume of tri-n-butyl phosphite, 80% by volume was recovered before the overhead evinced a negative test with respectto. the doctor. test.

In these distillations, a triaryl phosphite, a tri'aryl phosphate, 8; trialkyl phosphite and a trialkyl phosphate were utilized. However, only the trialkyl phosphite gave a beneficial result. 111e, results shown in Table I also indicate that at least a minimum amount is required in order to produce the beneficial elfcct in accordance with the process of this invention. This is shown by the distillations. in which- 0.1 volume percent and 0.3 volume percent of tri-n-butyl phosphite were. employed. In these distillation; the, yields of. doctor negative distillate were not increased. on the other hand, 0.4 volume percent was fully efiective.

In the distillation, which, was carried out in the ab.- n of an added selected organic phos hite, the residue remaining in the still after 90% by volume had. been distilled was. very malodorus and contained black solid material which was. dificnlt to remove. In contradistinctiou, the. residue remaining in the ill: Pot wherein the distillation was carried out. in the presence of. 0.4 volume percent. of ri-n-butyl Phosphite was clear, mild smelling, and aliquid, free of solid materials, which was easily handled for disposal. Purposes. This leads to a collaterellieature of this. in en ion. In. run 3., a second portion of Qxi a i y-sweet ned naphth wa admix d with the residue o ained n the. distillation of an ciddati y-sweetened naphtha in he pr n e of 5 vol me percent of tr i'-n-.'buty1 phosphite. This admixture. was distilled in, the manner employed in the foregoing in.- vesti'gati'on, and the results which were obtained were identical with those of the first run. In other words, 80% by volume was taken overhead before a positive efiect Withrespect to the doctor test was evinced in the distillation efliuent, Therefore, if desired, the initial. amount of selected organic phosphite employed in a batch distillation process can be utilized for more than one dis t llation.

1 It is necessary when re-using the. still pot residue to employ; a large excess of phosphite in the first run. (see run 5 In a continuous distillation, the best procedure would be. to feed the minimum eifective amount of phosphite continuously.

' Although the subject invention is especially adaptable to the production of industrial naphthas by the distilla- Table lion of an oxidatively-sweetened, full-boiling-range naph- Table I Volume Percent Overhead 1O 20 30 40 50 First Doctdrv sour Run Material added to Overhead Temperature at Out Point F.) Cut No. charge naphtha None 157 181 201 215 24c 264 290 5.0 ml. trl-n-but'yl I 7 (264-290) phosphite. 1.46 182 206 2.3 243 282 306. 340 9(306-340 ReslduefromRunZ--. 156 176 206 236 236 259 283 300 323 9(300-323; 4 0.5111311ill tetrl-n-butyl 146 182 202 222 240 263 288 316 348 9(315-348) D D 6 0.1 ml. tri-n-buty1 160 180 205 219. 232 269 290 6 (282-269) phosphlte. 84. 5.0 ml. tll-ll-blltyl 1,6}. 181 202 217 231 262 292 p 6 (231-262).

phosphate. t 10- 5.0 trl-tolyl Q1 05- 1 87 208.. 2.31 219 270 290 305 V 7 (270-290) I p a e. 11.... 0.3 trltbutyl phos- 158 182 205 220 234 262 292 307 340 6 (2341-262) p is. 12...-. 5.0 h mlim trl-phenyl 64 181 199 221 236 266 280 292 a 6 (236-206) p osp e. 13...- 04p trlrhutyl 121305? 65 180 202 217 252 275 292 318 352 9 (318-352) 1 e. t mtts ltssld froml nt-t 1. 3 1. 2 2 62 290 11223122).

tha or naphtha fraction, the invention has application in the refining or distillation of other light petroleum distillates boiling up to about 750 F. at atmospheric pressure, which have been previously oXidatively-sweetened. These include the light distillates, such as industrial petroleum naphthas and solvents; gasoline-type motor fuels and motor fuel blending components; kerosenes, etc.; and the middle distillates, such as diesel fuels, heater and furnace oils, etc., which are subjected to elevated temperatures whereby the sulfur constituents of the hydrocarbon fraction are decomposed to form sulfur compound which impart undesirable odor and corrosive properties to the fraction. Although the foregoing illustrative example has been directed to the use of the instant invention in a batch-wise distillation process, it is evident that the invention has application in the treatment of sulfur-containing hydrocarbon fractions in refining processes which are carried out at elevated temperatures conducive to the decomposition of the sulfur compounds contained in said fraction to produce undesirable sulfurcontaining products. Accordingly, a number of modifications and variations of the instant invention can be made by those skilled in the art to which this invention pertains Without departing from the scope of this invention as defined in the appended claims.

Accordingly, we claim as our invention:

1. In the fractional distillation of an oxidativelysweetened, hydroca'bon fraction boiling within the naphtha boiling range and containing organic sulfur compounds, including disulfides, at an elevated temperature normally effective for the conversion of said compounds to produce doctor-positive products, the improvements wherein said conversion is minimized which comprises carrying out the distillation at said temperature in the presence of an added amount of an oil-soluble, saturated organic phosphite from the group consisting of alkyl and cycloalkyl phosphites and having a boiling point at least as high as the end boiling point of the hydrocarbon fraction being distilled, the amount of said organic phosphite being not less than about 0.4% by weight, based on the amount of said hydrocarbon fraction being fractionally distilled.

2. In the fraction distillation of an oxidatively-sweetened, hydrocarbon fraction boiling within the naphtha boiling range and containing organic sulfur compounds, including disulfides, at an elevated temperature normally effective for the conversion of said compounds to produce doctor-positive products, the improvement wherein said conversion is minimized which comprises carrying out the distillation at said temperature in the presence of an added amount of an oil-soluble, saturated organic phosphite from the group consisting of alkyl and cycloalkyl phosphites and having a boiling point at least as high as the end boiling point of the hydrocarbon fraction being distilled, the amount of said organic phosphite being about 0.41% by weight, based on the amount of said hydrocarbon fraction being fractionally distilled.

3. In the distillation of an oxidatively-sweetened, hydrocarbon fraction boiling within the naphtha boiling range and containing organic sulfur compounds, including disulfides, at an elevated temperature normally effective for the conversion of said compounds to produce doctor-positive products, the improvements wherein said conversion is minimized which comprises carrying out the distillation at said temperature in the presence of an added amount of an oil-soluble, alkyl phosphite having a boiling point at least as high as the end point of the hydrocarbon fraction being distilled, the amount of said organic phosphite being not less than about 0.4% by weight, based on the amount of said hydrocarbon fraction being distilled.

4. In the fractional distillation of an oxidativelysweetened hydrocarbon fraction boiling within the naphtha boiling range and containing organic sulfur compounds, including disulfides at an elevated temperature normally effective for the conversion of said compounds to produce doctor-positive products, the improvement wherein said conversion is minimized which comprises carrying out the fractional distillation at said temperature in the presence of an added amount of an oilsoluble, alkyl, phosphite hav, mg a boiling point at least as high as the end boiling point of the hydrocarbon fraction being fractionally distilled, the amount of said aliphatic phosphite being within the range of about 0.4-1% by weight of the amount of hydrocarbon fraction being distilled.

5. In a fractional distillation process in accordance with claim 4 in which said alkyl phosphite is tributyl phosphite.

6. In the fractional distillation of an oxidativelysweetened, hydrocarbon fraction boiling Within the naphtha boiling range and containing organic sulfur compounds, including disulfides, at an elevated temperature normally effective for the conversion of said compounds to produce doctor-positive products, said fraction having been oXidatively-sweetened in a copper chloride sweetening process, the improvement wherein said conversion is minimized which comprises carrying out the distillation at said temperature in the presence of an added amount of an oil-soluble, saturated organic phosphite from the group consisting of alkyl and cycloalkyl phosphites and having a boiling point at least as high as the end boiling point of the hydrocarbon fraction being distilled, the amount of said organic phosphite being not less than about 0.4% by weight, based on the amount of said hydrocarbon fraction being fractionally distilled.

7. In the fractional distillation of an oxidativelysweetened, hydrocarbon fraction boiling within the naphtha boiling range and containing organic sulfur compounds, including disulfides, at an elevated temperature normally effective for the conversion of said compounds to produce doctor positive products, said fraction having been oxidatively sweetened in a copper chloride sweetening process, the improvement wherein said conversion is minimized which comprises carrying out the fractional distillation at said temperature in the presence of an added amount of an oil-soluble, alkyl phosphite having a boiling point at least as high as the end boiling point of the hydrocarbon fraction being fractionally distilled, the amount of said alkyl phosphite being within the range of about 0.41% by weight of the amount of hydrocarbon fraction being distilled.

8. In a fractional distillation process in accordance with claim 7 in which said alkyl phosphite is tributyl phosphite.

9. In the fractional distillation of a hydrocarbon fraction boiling within the naphtha boiling range and oXidatively sweetened by contact with an admixture of copper chloride and an acid treated, montmorillonite type clay whereby there is producd a doctor-sweet hydrocarbon fraction containing organic sulfur compounds, including disulfides, susceptible to decomposition at an elevated temperature, the improvement which comprises carrying out the fractional distillation at an elevated temperature in the presence of an added amount of an oilsoluble, saturated phosphite from the group consisting of alkyl and cycloalkyl phosphites and having a boiling point at least as high as the end boiling point of the the hydrocarbon fraction being fractionally distilled, the amount of said organic phosphite being within the range of about 0.41% by Weight of said hydrocarbon fraction.

References Cited in the file of this patent UNITED STATES PATENTS 2,413,353 Hunter et al. Dec. 31, 1946 2,427,173 Withrow Sept. 9, 1947 2,775,545 Sandner et al. Dec. 25, 1956 2,793,983 Ayers May 28, 1957 

1. IN THE FRACTIONAL DISTILLATION OF AN OXIDATIVELYSWEETENED, HYDROCARBON FRACTION BOILING WITHIN THE NAPHTHA BOILING RANGE AND CONTAINING ORGANIC SULFUR COMPOUNDS, INCLUDING DISULFIDES, AT AN ELEVATED TEMPERATURE NORMALLY EFFECTIVE FOR THE CONVERSION OF SAID COMPOUNDS TO PRODUCE DOCTOR-POSITIVE PRODUCTS, THE IMPROVEMENTS WHEREIN SAID CONVERSION IS MINIMIZED WHICH COMPRISES CARRYING OUT THE DISTILLATION AT SAID TEMPERATURE IN THE PRESENCE OF AN ADDED AMOUNT OF AN OIL-SOLUBLE, SATURATED ORGANIC PHOSPHITE FROM THE GROUP CONSISTING OF ALKYL AND CYCLOALKYL PHOSPHITE AND HAVING A BOILING POINT AT LEAST AS HIGH AS THE END BOILING POINT OF THE HYDROCARBON FRACTION BEING DISTILLED, THE AMOUNT OF SAID ORGANIC PHOSPHITE BEING NOT LESS THAN ABOUT 0.4% BY WEIGHT, BASED ON THE AMOUNT OF SAID HYDROCARBON FRACTION BEING FRACTIONALLY DISTILLED. 